1. Field of the Invention
This invention relates to spatial light modulators, more particularly to semiconductor spatial light modulators.
2. Background of the Invention
Spatial light modulators typically consist of linear or area arrays of cells that are individually addressable. Examples of these are liquid crystal display cells, electro-optic modulators, magneto-optic modulators, and digital micromirrors (also known as deformable mirror devices). Spatial light modulators typically have some type of addressing circuitry that allows each cell to be individually addressed. Liquid crystal displays for example, have electrodes that allow the crystal material to either transmit or prevent transmission, when these devices operate in the transmissive mode. These electrodes may also have some type of memory structure associated with them that allows the electrode to hold the data that determines the state of each cell.
A problem exists for spatial light modulators that rely on semiconductor material in which to build their addressing circuitry. A light source must be used that impinges directly upon the cells. Light incident upon semiconductors, such as silicon, generates photocarriers. This can lead to the addressing and memory circuitry, if used, having leakage currents caused by these photocarriers.
Photocarrier generation can be reduced through the use of double-level metal addressing lines for dynamic random-access-memory (DRAM). This process, which typically involves using one level of metal for horizontal interconnects, and another level of metal for vertical interconnects such as data lines, address lines and power supplies, does cover a large portion of the substrate. Unfortunately, the amount of light used with spatial light modulators can overcome this coverage, and leakage-causing photocarriers are still a problem for semiconductor light modulators.